Madden-Julian Oscillation (MJO)

The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal tropical variability, an eastward-propagating envelope of enhanced and suppressed deep convection coupled to large-scale circulation. It travels at roughly 5 m/s across the Indian and Pacific warm-pool oceans with a period of 30 to 90 days, tracked by the Real-time Multivariate MJO (RMM) index built from outgoing longwave radiation and zonal winds. Active phases modulate monsoon bursts, tropical cyclogenesis, and atmospheric rivers, and can trigger oceanic Kelvin waves that influence ENSO development.